1. Field of the Invention
The present invention relates to a tone waveform reproduction apparatus, and in particular to a tone waveform reproduction apparatus that is employed for electronic musical instruments.
2. Description of the Related Arts
In an electronic musical instrument for storing a tone waveform in a memory and reading it for reproduction, when a pitch is changed for reproduction of a tone waveform, a frequency band included in the original waveform that is reproduced is shifted. Therefore, when the pitch is raised, a reproduced tone waveform is shifted to a frequency higher than the original frequency band, so that the sound of the resultant tone sounds high. On the other hand, when the pitch is decreased, the reproduced tone waveform is shifted to a frequency lower than the original frequency band, so that the sound of the resultant tone sounds low.
Conventionally, to resolve this problem, a method is employed for varying a cutoff frequency of a filter in consonance with keys on a keyboard, i.e., a key scaling method. With this key scaling method, the above problem can be considerably resolved when a single basic tone waveform is used for all the keys on a keyboard.
However, when a plurality of basic tone waveforms, i.e., a plurality of samples, are used in consonance with tone ranges, a reproduced frequency for a tone waveform corresponding to each key is as is indicated by a solid line a in FIG. 5. And if the key scaling b is applied for the reproduced frequency, the frequency is as is indicated by broken line c. It should be noted that the reproduced frequencies a and c are properties obtained after conventional cutoff control was executed at cutoff frequency fco.
As is apparent from the reproduced frequency a, at a point where samples are switched, i.e., where tone ranges are switched, a sample in the low range sounds high while a sample in the high range sounds low. Furthermore, as is apparent from the reproduced frequency c, even when key scaling is applied for the reproduced frequency a, the reproduced frequency is discontinuous at a point where the samples are switched, so that a timbre is rendered unnatural. As is evident from the above description, a conventional cutoff control cannot resolve the problem arising from a timbre being rendered unnatural at a point where samples are switched.